1. Field of the Invention
This invention relates to a liquid-dispensing apparatus which can be applied to handling of a liquid for research, development, production and inspection in science and engineering, medical science and production techniques.
2. Discussion of the Background
As one example of a conventional apparatus, a partially improved apparatus of the apparatus disclosed in Japanese Provisional Patent Publication No. 102151/1994 (U.S. patent application Ser. No. 08/118,328), which is a previous invention by the present inventors, is shown in FIG. 5 and FIG. 6.
In a conventional liquid-dispensing apparatus which is used for clinical tests, in order to prevent contamination between samples to be tested, a sampling chip which is not contaminated with a previous sample is required to be used for each dispension. Accordingly, a sampling chip such as a plastic molded product prepared by injection molding has been generally used, but such a sampling chip is extremely expensive.
As a sample-sucking mechanism, there may be mostly used a mechanism using a cylinder. An apparatus using such a mechanism is expensive and it is necessary to fit the above sampling chip to a nozzle at the end of a cylinder each time. When a liquid is sucked by a cylinder, even a slight failure of fitting causes leakage of air at a fitting portion so that there are drawbacks in that a reduced pressure state may not be maintained and inaccuracy in the amount sucked will occur.
In a roller system previously proposed by the present inventors as an improvement of such a sample-sucking mechanism, as shown in FIG. 5 and FIG. 6 which is a sectional view of FIG. 5 cut along with A-A' line, a pressing roller 50 is driven by a driving portion not shown in the figure, and a moving amount of the pressing roller 50 with a pinion 52 which moves while rotating determines a sample-sucking amount. The length of a rack 51 is required to have a length at least equal to a length of pressing a tube+.alpha., whereby it is difficult to miniaturize the whole structure.
That is, the rack 51 and the pinion 52 are provided in order to prevent the tube 2 from being pulled by the pressing roller 50 and slipped greatly when the pressing roller 50 rotates while pressing a tube 2. When the pressing roller 50 is moved, the pinion 52 provided on the same axis of the pressing roller 50 is rotated by the rack 51 so that the pressing roller 50 is also rotated, whereby almost no slippage of the tube is caused.
However, in such a system, a thickness of the tube 2 pressed by pressing actually causes a difference of a pitch circle. Therefore, when the pressing roller 50 moves while pressing the tube 2, the tube 2 slightly slips, whereby an adverse influence an conveying occurs. For this reason, a tube having a different wall thickness cannot be used.